This invention relates to switching power converter circuits and methods and, in particular, relates to a converter circuit and method with an auxiliary supply voltage.
Switching power converters are used in a wide variety of applications to convert electrical power from one form to another form. For example, dc/dc converters are used to convert dc power provided at one voltage level to dc power at another voltage level. One application in which dc/dc converters are used is to provide a supply voltage to microprocessors and other digital devices. To provide this supply voltage, transformer coupled converters are commonly used, especially when isolation between the input and output voltages is required, or when the input voltage to the converter is much higher than the output voltage which is supplied to the microprocessor.
In typical transformer coupled converters, an input voltage is applied to a primary winding and electrical power is transferred through a transformer core to a rectification circuit coupled to a secondary winding. Secondary current flows in the secondary winding, and the secondary current is rectified and used to charge an output capacitor of the converter circuit. In a simple converter circuit, the rectifier is a diode.
Newer microprocessors require lower supply voltages, for example, in the range of one to three volts. In order to promote efficient operation at this output voltage range, synchronous rectifiers have been employed instead of diodes in rectification circuits of dc/dc converters. However, synchronous rectifiers often require a gate drive voltage which is higher (e.g., 5-10 volts) than the converter output voltage which is supplied to the microprocessor. Gate drive amplifiers and other control circuitry on the secondary side also may need a higher supply voltage.
Therefore, a need exists for a converter circuit that is capable of providing an auxiliary output voltage to provide power for devices that operate at a voltage level that is different than the voltage level of the main output voltage of the converter circuit.
According to a first preferred aspect, a converter circuit comprises a transformer core, a primary winding, a secondary winding, a main rectification circuit, an auxiliary rectification circuit. The primary winding and the secondary winding are wound around the transformer core. The main rectification circuit and the auxiliary rectification circuit are both connected to the secondary winding and produce output voltages having different magnitudes.
According to a second preferred aspect, a dc/dc converter circuit comprises a transformer core, a primary winding, a secondary winding, a main rectification circuit, an auxiliary rectification circuit, a drive circuit, and a drive control circuit. The primary winding and the secondary winding are wound around the transformer core. The main rectification circuit is connected to the secondary winding. The main rectification circuit further comprises a first output capacitor and a rectifier that controls current flow through the first output capacitor. An output voltage of the main rectification circuit is produced across the first output capacitor.
The auxiliary rectification circuit is connected to the secondary winding. The auxiliary rectification circuit further comprises a second output capacitor. An output voltage of the auxiliary rectification circuit is produced across the second output capacitor. The output voltage of the auxiliary rectification circuit has a magnitude which is different than a magnitude of the output voltage of the main rectification circuit.
The drive circuit is coupled to receive a supply voltage. The drive control circuit is coupled to the drive circuit and controls the drive circuit to apply a pulse width modulated dc voltage to the primary winding. The drive control circuit controls the rectifier to synchronize operation of the rectifier to the pulse width modulated voltage. The drive control circuit is connected to receive the output voltage produced by the auxiliary rectification circuit, the drive control circuit using the output voltage produced by the auxiliary rectification circuit to produce a control signal for the rectifier. The control signal has a voltage magnitude which is determined at least in part by the magnitude of the output voltage of the auxiliary rectification circuit.
Other objects, features, and advantages of the present invention will become apparent to those skilled in the art from the following detailed description and accompanying drawings. It should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the present invention, are given by way of illustration and not limitation. Many modifications and changes within the scope of the present invention may be made without departing from the spirit thereof, and the invention includes all such modifications.